Method and apparatus for preparing powdered coal for injection into a blast furnace



May 10, 1956 .1. c. AGARWAL METHOD AND APPARATUS FOR PREPARING POWDEREDCOAL FOR INJECTION INTO A BLAST FURNACE Fild NOV. 8, 1962 AttorneyUnited States .Patent 'O This invention relates to an improved methodand u apparatus for preparing powdered coal for injection into a blastfurnace.

l The most common practice in operating a blast furnac is to supply allthe necessary fuel in the form of coke charged with the burden. However,it is known that part of the coke usually required can be replaced withfuel injected with the blast at the tuyeres. This fuel can be eithersolid (e.g., powdered coal), liquid or gaseous, and its combustionsupplies at least part of the heat required to operate the furnace. Cokecharged with the burden has other functions, such as furnishing carbonfor reducin-g ore and physically supporting the burden. Fuel injected atthe tuyeres cannot serve such purposes, but any replacement of the morecostly coke with cheaper fuels leads to worthwhile savings. Whenpowdered coal is' used as the injected fuel, it must irstlbe carefullyprepared by drying and sizing.

An object of the present invention is to provide an improved method andapparatus for drying and sizing powdered coal to enable it to beinjected into the tuyeres of a blast furnace as replacement for coke.

apparatus for preparing powdered coal in which sensible heat in the topgas from a blast furnace is utilized for drying the coal in a fluidizedbed.

A further object is to provide a method and apparatus which offer theforegoing advantages, and in which the gas used for drying the coalsubsequently is cleaned and u-sed for injecting the coal into thefurnace.

In the drawing:

The single figure is a schematic flowsheet of my method and apparatus.

My apparatus includes a conventional fluidized bed dryer 10 whi-chcontains a perforate partition 12 in its lower portion for supporting abed B ofrninus 1/2 inch or smaller coal particles. A screw conveyor 13continuously feeds coal fines to the dryer from a storage bin 14. Inaccordance with my invention, I introduce -top gas from a blast furnace(not shown) via a line 15 to the bottom of the dryer, where the gas actsto fluidize the bed. This gas commonly is at a temperature within therange of about 350 to 600 F. and a pressure of about 2 to 30 p.s.i.g.Sensible heat in the gas serves to maintain coal in the bed at atemperature of about 250 to 350- F. and thus dri-ves off moisture,leaving the coal with a maximum moisture content of about 4 percent. y Ipreferably control the temperature automatically with atemperature-sensing element 16 in the dryer, a controller 17 connectedto said element and an adju-stable valve 18 which is connected to line15 and operated by said controller, all which per se are of conventionalconstruction. Valve 18 routes excess top gas through a bypass 19.Alternatively, I can measure the bed temperature and adjust valve 18manually.

Dried coal discharges from bed B via a line 20 which leadsto afractionating screen 21. Preferably line 20 is equipped with anautomatic mechanism 22 for controlling the bed level in the dryer, asknown in the art. Screen 21 has openings of a size to pass particlessuit-able for injection into the furnace, commonly minus 1A; inch orminus 1/16 inch. Undersize particles from the screen go to a storagevessel 23. Oversize particles from the screen go to a pulverizer 24 andthence back to the screen in a closed circuit arrangement. Contaminatedand moistureladen olf-gas discharges from the top of the dryer via aline 25 which leads to a dust collector 26, for example a cyclone. Aline 27 carries dust recovered from the gas in the dust collector toscreen 21, where it joins the dried coal from line 20.

Gas from the dust collector 26 and from the bypass 19 goes to aconventional venturi scrubber 28 to which Water is introduced via a line29. The scrubber is connected to a conventional entrainment separator30. Waste slurry from the separator goes to a thickener (not shown),while the gas goes to a cooler 31 where it is cooled to a temperature ofabout F. A line 32, which contains a conventional automatic flowcontroller 33, carries a portion of the gas from the cooler to acompressor V34, where it is compressed -to approximately p.s.-i.g. Aline 35 carries the remainder of the gas from the cooler to blastfurnace stoves (not shown) or other equipment where the gas is consumedin the usual way. A line 36, which contains a conventional automaticpressure regulator 37, carries gas from the compressor 34 to aconventional gas dryer 38, where it is dried to a dew point of about 0to v 20 F. VA line 39 carries gas from the dryer 38 to a gas holder 40.A line 41 carries gas from the holder 40 to the coal storage vessel 23.Gas in the last-named line picks up dried powdered coal from the vesseland transports it to the blast furnace tuyeres (not shown) where it isinjected into the furnace. In this manner the hydrogen and carbonmonoxide remaining in the top gas likewise `are utilized effectively inthe fu-rnace. I use approximately 1/2 to 3 cu. ft. of gas for injectingeach pound of coal.

My invention may be modified by heating the compressed and dried gasfrom the dryer 38 to a temperature up to about 800 F. to eliminateexcessiveheat load on the blast furnace. In addition, the compressed topgas can be purified by any conventional method to eliminate carbondioxide. 'The removal of carbon dioxide improves the efficiency of theblast furnace, because carbon is required to reduce the carbon dioxideto carbon monoxide. The drawing schematically indicates lconventionaldevices 42 and 43 for preheating the gas and removing carbon dioxide.Also, conventionally compressed and dried air instead of blast-furnacetop gas may be used to convey the coal particles to the blast furnace.

A specific example of the practice of my invention is as follows:

I operated a blast furnace having a 23-ft. hearth vdiameter with a hotblast at 65,000 cu. ft./ min` having a ternperature of approximately1650 F. vI produced approximately 1600 tons/day of hot metal with a cokerate of approximately 1260 lb./THM. During this operation, I obtainedapproximately 90,000 cu. ft./min. of top gas at a pressure ofapproximately 9 p.s.i.g. I used minus 1/z-in. Maple Creek coal forinjection, and dried this coal from a 10 percent to a 3 percent moisturecontent at a rate of 10 tons/ hr. in a fluidized-bed dryer. I maintainedthe drying atmosphere at 250 F. by regulating the amount of top gasintroduced to the dryer. The top gas leaving the blast furnace was at atemperature of 410 F. I controlled the gas flow to the dryer so thatapproximately 17,500 cu. ft./ min. of top gas passed through it. Theremainder of the top gas bypassed the dryer and combined with themoisture-ladened top gas leaving the cyclone. I took approximately 400cu. ft./min. of this top gas, compressed it to approximately 100p.s.i.g., and then dried it in a conventional silica-gel dryer to a dewpoint of 10 F. I used this gas to inject 9.28 ton's/ hr. of dried andpulverized coal into the blast furnace.

The advantages of my method are apparent from the above description ofthe operation. By using the blastfurnace top gas as the drying medium,the need for an external heat source is eliminated. Also, additionalequipment is not required to clean the gas leaving the dryer, since itmay be combined With the top gas bypassing the dryer and thus processedby the equipment conventional to blast-furnace installations. Theexplosion hazard usually associated with storing dried and pulverizedcoal is eliminated by employing an atmosphere of top gas in thecoal-storage vessels. In addition, the gas used for injection iscompatible with the blast-furnace process.

While I have shown and described only a single embodiment of myinvention, it is apparent that modifications may arise. Therefore, I donot wish to be limited to the disclosure set forth but only by the scopeof the appended claims.

I claim:

1. A method of preparing coal for injection into the tuyeres of a blastfurnace comprising feeding coal ines to a fluidized bed dryer,introducing top gas from a blast furnace to the dryer to iiuidize thecoal fines, utilizingy sensible heat in this gas to drive moisture fromthe coal, discharging dried coal from the dryer, screen-sizing the driedcoal to separate out undersize coal particles having a maximum size ofabout ls-in. and suitable for injection, pulverizing the oversize coalparticles for further screensizing, cleaning, compressing and drying theoit-gas from the dryer, and utilizing this olf-gas for injecting theundersize particles.

2. A method of preparing coal for injection into the tuyeres of a blastfurnace comprising feeding coal iines to a iluidized bed dryer,introducing top gas from a blast furnace to the dryer to lluidize thecoal lines, said gas being at a temperature of about 350 to 600 F. and apressure of about 2 to 30 p.s'.i.g., utilizing sensible heat in this gasto drive moisture from the coal and thus lower its moisture content to amaximum of about 4 percent, discharging dried coal from the dryer,screen-sizing the dried coal to separate out coal particles having amaximum size of about 1s-in. and suitable for injection, pulverizingthel oversize coal particles, and again screen-sizing the pulverizedcoal in a closed circuit arrangement.

3. A method as defined in claim 2 in which off-gas from the dryer iscleaned, compressed, dried and utilized in part for injecting theundersize coal particles.

4. A method of preparing and injecting coal into the tuyeres of a blastfurnace comprising feeding coal nes to a tluidized bed dryer,introducing a portion of the top gas from a blast furnace to the dryerto rluidize the coal ines, said gas being at a temperature of about 350to 600 F. and a pressure of about 2 to 30 p.s.i.g., utilizing sensibleheat in this gas to drive moisture from the coal and thus lower itsmoisture content to a maximum of about 4 percent, discharging dried coaland off-gas from the dryer, screen-sizing the dried coal to separate outcoal particles having a maximum size of about 1s-in. and suitable forinjection, pulverizing the oversize coal particles, again screen-sizingthe pulverized coal in a closed circuit arrangement, collecting dustfrom said off-gas, combining another portion of the top gas with saidoff-gas, cleaning and cooling the resulting combined gas, compressingand drying a portion of the cleaned and cooled gas, and utilizing thelast-named portion for injecting the dried and sized coal particles intothe tuyeres.

5. A method as dened in claim 4 in which the lastnamed portion of thecleaned and cooled gas is preheated to a maximum temperature of about800 F.

6. A method as defined in claim 4 in which the lastnamed portion of thecleaned and cooled gas is puried to eliminate carbon dioxide.

7. An apparatus for preparing coal for injection into the tuyeres of ablast furnace comprising a liuidized bed dryer, means operativelyconnected With said dryer for feeding coal fines thereto, meansoperatively connected with said dryer for introducing blast furnace topgas thereto to fluidize the coal lines and supply sensible heat fordriving ofr moisture, a fractionating screen, means for transferringdried coal fines from said dryer to said screen, means for collectingundersize particles from said screen suitable for injection, apulverizer, means for transferring oversize particles from said screento said pulverizer and pulverized particles back to said screen in aclosed circuit arrangement, means operatively connected with said dryerfor cleaning, compressing and drying off-gas therefrom, and means forutilizing this off-gas for injecting undersize coalparticles into theblast furnace tuyeres.

References Cited by the Examiner UNITED STATES PATENTS 1,628,609 5/ 1927Newhouse 110--106 2,103,453 1 2/ 1937 Graemiger 110-28 2,560,807 7/1951Lobo 241-24 2,841,125 7/1958 Falla 110-106 X 2,939,411 6/ 1960 Priestley11028 3,192,068 6/1965 Brandt 34-10 X FOREIGN PATENTS 865,221 2/ 1941France. 369,330 3/ 1932 Great Britain.

ALDEN D. STEWART, Primary Examiner.

NOMAN YUDKOFF, WILLIAM F. ODEA,

Examiners.

W. C. EVERETT, D. A. TAMBURRO,

Assistant Examiners,

1. A METHOD OF PREPARING COAL FOR INJECTING INTO THE TUYERES OF A BLASTFURNACE COMPRISING FEEDING COAL FINES TO A FLUIDIZED BED DRYER,INTRODUCING TOP GAS FROM A BLAST FURNACE TO THE DRYER TO FLUIDIZE THECOAL FINES, UTILIZING SENSIBLE HEAT IN THIS GAS TO DRIVE MOISTURE FROMTHE COAL, DISCHARGING DRIED COAL FROM THE DRYER, SCREEN-SIZING THE DRIEDCOAL TO SEPARATE OUT UNDERSIZE COAL PARTICLES HAVING A MAXIMUM SIZE OFABOUT 1/8-IN. AND SUITABLE FOR INJECTION, PULVERIZING THE OVERSIZE COALPARTICLES FOR FURTHER SCREENSIZING, CLEANING, COMPRESSING AND DRYING THEOFF-GAS FROM THE DRYER, AND UTILIZING THIS OFF-GAS FOR INJECTING THEUNDERSIZE PARTICLES.